A conventional window frame has an upper flange, a lower flange, and two side flanges that are generally fastened directly on to plywood sheathing of a wall of a building during installation. Insulation sheets are usually disposed directly on the outer surface of the upper flange and plywood is used to cover the outer surface of the insulation sheets. Traditionally, a lower (river) flashing is disposed adjacent the lower edge of the window frame, on the outer surface of the lower flange. An upper flashing is generally fastened to the plywood sheathing of the wall through the upper flange.
Buildings, including their windows, are exposed to water under various weather conditions. The water that buildings are exposed to includes for example rain water and water from condensation, melted ice, snow, and frost. With the conventional window and method of window installation, water can seep behind the upper flange and will trickle down between the flashing/upper flange and the plywood at the top of the window, which can cause the plywood to deteriorate. Further water can seep behind the lower flashing through the lower flange, into the plywood sheathing, which can also cause the plywood to deteriorate.
Further, the placement of the insulation sheets can prevent water from flowing down the flange, causing water to seep into the plywood behind the flange and the plywood covering the insulation sheets. Water from the plywood sheathing can also seep into 25 other parts of the wall, such as studs and insulation materials. Water damage to the wood components of the wall can compromise the strength and integrity of the wall. Further, mold can easily develop in damp areas inside the wall, which can pose a serious health threat.